Overview

Hemophagocytic lymphohistiocytosis (HLH) is a condition in which the body makes too many activated immune cells (macrophages and lymphocytes).[1] People with HLH usually develop symptoms within the first months or years of life which may include fever, enlarged liver or spleen, cytopenia (lower-than-normal number of blood cells), and neurological abnormalities.[2][3] HLH may be inherited in an autosomal recessive manner or it can have non-genetic causes in which case it is called acquired HLH. There are five subtypes of inherited HLH which are designated familial HLH, types 1-5. Each subtype is caused by a change (mutation) in a different gene. The genetic cause of type 1 is currently unknown. Types 2-5 are caused by mutations in the PRF1 gene, the UNC13D gene, the STX11 gene and the STXBP2 gene, respectively.[4] Treatment depends on a number of factors, including the severity of symptoms, the age of onset, and the underlying cause of the condition.[4][5]